After I had fallen for a cheap part, which on the RS232 side TTL level spending (0-5V) I tried to Digitus and works fine: - FTDI / FT232RLA chip - Signal level measured -5.5V / + 5.5V so within the RS232 specification - Hardware handshake lines are busy and work - Speed up almost 1Mbit / s can be set, on the oscilloscope I can see the data packets, looks clean. Communication I can for lack of suitable remote but not consider the speed. The only other party with whom I speak straight, requires only 4800 baud.